What Happens When a Furnace Pressure Switch Goes Bad?

Turning on an oil or gas furnace initiates a sequence of events that produce heat and send it through the ducts to warm your home. But what happens when a furnace pressure switch goes bad? Like any other part of the furnace, the pressure switch must work correctly to ensure that the furnace operates safely. If it stops working, the furnace won’t produce heat, and you’ll feel cool or room-temperature air flowing from the ducts. 

Although you may be able to identify a furnace pressure switch problem with an error code, it’s best to leave repairs to a professional. Working on the switch involves working around high voltage, heat, and moving parts. For safety, call JC Heating & Cooling for expert heating repair in Hodgkins, IL, and the surrounding area at 708-968-3131 to get your furnace running smoothly again. 

What Is a Furnace Pressure Switch?

The furnace pressure switch is a safety feature that prevents dangerous exhaust from cycling back into the system, gas leaks, and constant cycling if there’s another mechanical malfunction. The switch, which normally remains open, senses negative pressure or suction when the furnace inducer motor comes on and automatically closes. This process happens almost instantaneously, and as long as the switch closes as it should, the startup process will continue, and the furnace will come on and start producing heat. 

What happens when a furnace pressure switch goes bad is it doesn’t sense the negative pressure, so it remains open. Most furnaces will abort the startup process and try again after a few minutes. If the switch doesn’t engage after three to five tries, the furnace goes into safety lockout mode, and you will not get any heat from the system.

Different types of furnaces have varying pressure switch configurations. Most conventional furnaces have a single hose connecting the switch to the inducer fan, while a two-stage furnace has two switches, and a modulating furnace can have three pressure switches. 

Identifying a Faulty Furnace Pressure Switch 

As mentioned, some furnaces have an LED panel that indicates problems. If the error code shows that the pressure switch is open, the unit is in safety lockout mode, and you may need a replacement pressure switch. 

When you can’t find or interpret the error code, you may be able to identify a pressure switch issue just by listening to the furnace. When it comes on, listen for a distinctive clicking sound right after the fan starts. If you don’t hear the click, the switch isn’t engaged, and the furnace needs repair. 

The Most Common Reasons Furnace Pressure Switches Fail

Furnace pressure switches can fail for many reasons. Some of the most common include:

  • Age-related wear and tear, which can cause the switch to make incorrect readings and faulty furnace cycling 
  • Electrical shorts 
  • Damage to the suction hose or diaphragm 
  • Problems with the inducer fan, including a bad motor, a motor malfunction that causes it to blow too slowly, or a fan blockage
  • Dirt and dust buildup blocking the switch
  • Loose or faulty electrical connections
  • Loose suction tube
  • Blockage in the flue or chimney 
  • Water in the inducer fan housing

Fixing a Bad Furnace Pressure Switch 

If an HVAC tech discovers a damaged or malfunctioning pressure switch, replacing it may be the best solution. However, because the pressure switch issues can stem from other problems within the furnace, they may need to make additional repairs or replace the entire furnace. For example, furnace inducer fans receive electric currents from control boards, which signal them to turn on; a short or another electrical issue prevents the fan from working and the switch from closing. 

Assuming that other issues in the furnace aren’t the cause of the switch failure, replacing a furnace pressure switch is a relatively simple and inexpensive task. Leave this work to a professional to ensure correct installation and streamline the process. It’s not always easy for homeowners to find the correct part, but a professional will likely have easy access to it, preventing delays. 

Trust JC Heating & Cooling for Help with Furnace Problems 

If you have more questions about what happens when a furnace pressure switch goes bad or suspect your furnace needs this repair, call the experts from JC Heating & Cooling for help. Their experienced, trained, and licensed team can help with any problem in Hodgkins, IL, whether your furnace is leaking water or will not turn on. Call them at 708-968-3131 to schedule an appointment.